Surface modified unit cell lattice structures for optimized secure freeform fabrication

ABSTRACT

Aspects of the present disclosure relate generally to preparing models of three-dimensional structures. In particular, a model of a three-dimensional structure constructed of porous geometries is prepared. A component file including a porous CAD volume having a boundary is prepared. A space including the porous CAD volume is populated with unit cells. The unit cells are populated with porous geometries having a plurality of struts having nodes on each end. The space is populated with at least one elongated fixation element extending beyond the boundary to produce an interlocking feature enabling assembly or engagement with a mating structure.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part of U.S. patentapplication Ser. No. 13/441,154, filed Apr. 6, 2012, the disclosure ofwhich is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to preparing computer-generatedmodels of porous structures. In particular, the surfaces ofcomputer-generated models of structures may be modified through movementand removal of struts and nodes of porous geometries near the surface toproduce surfaces conforming to the surfaces of intended physicalstructures being modeled.

BACKGROUND OF THE INVENTION

The field of free-form fabrication has seen many important recentadvances in the fabrication of articles directly from computercontrolled databases. These advances, many of which are in the field ofrapid prototyping of articles such as prototype parts and mold dies,have greatly reduced the time and expense required to fabricatearticles, particularly in contrast to conventional machining processesin which a block of material, such as a metal, is machined according toengineering drawings.

One example of a modern rapid prototyping technology is a selectivelaser sintering process. According to this technology, articles areproduced in layer-wise fashion from a laser-fusible powder that isdispensed one layer at a time. The powder is sintered, by theapplication of laser energy that is directed in raster-scan fashion toportions of the powder layer corresponding to a cross section of thearticle. After the sintering of the powder on one particular layer, anadditional layer of powder is dispensed, and the process repeated, withsintering taking place between the current layer and the previously laidlayers until the article is complete. Detailed descriptions of theselective laser sintering technology may be found in U.S. Pat. No.4,863,538, U.S. Pat. No. 5,017,753, U.S. Pat. No. 5,076,869 and U.S.Pat. No. 4,944,817, the entire disclosures of which are incorporated byreference herein. Similarly, a detailed description of the use ofselective laser melting technology may be found in U.S. patentapplication Ser. No. 10/704,270, filed on Nov. 7, 2003, now U.S. Pat.No. 7,537,664 (“the '664 Patent”), the disclosure of which isincorporated by reference herein. The selective laser melting andsintering technologies have enabled the direct manufacture of solid orporous three-dimensional articles of high resolution and dimensionalaccuracy from a variety of materials including wax, metal powders withbinders, polycarbonate, nylon, other plastics and composite materials,such as polymer-coated metals and ceramics.

The invention claimed in the '664 Patent was the first of manyinventions assigned to Howmedica Osteonics Corporation, who has been apioneer in porous surface and porous structure formation, specificallyfor use in orthopedics. For instance, other applications in this area,such as U.S. patent application Ser. No. 11/027,421 filed on Dec. 30,2004 (“the '421 Application”), and U.S. patent application Ser. No.12/846,327 filed on Jul. 29, 2010 (“the '327 Application”), the entiredisclosures of which are hereby incorporated by reference herein, havetaught the generation of a population of porous geometry, a mathematicalrepresentation of the portion of geometry of the porous structure to bebuilt within a region defined by predetermined unit cells or imaginaryvolumes that are organized to fill and form a predetermined buildgeometry, or model build structure, which may be used to produce a nearnet-shape of an intended porous tissue in-growth structure. Thepredetermined build geometry, or overall computer-aided design (CAD)geometry, may refer to the mathematical or pictorial representation(such as that on a computer display) of the extent or outer boundary ofan intended physical structure to be manufactured. In the case ofphysical components that include both porous material and solidmaterial, the model build structure may be an assembly of solid andporous CAD volumes that model the outer boundaries of the respectivesolid and porous materials intended to be manufactured. Furthermore,these applications teach the randomization of the position ofinterconnected nodes, or points of intersection between two struts orbetween a strut and a substrate, that define each of the porousgeometries while maintaining the interconnectivity between the nodes. Aspreviously taught, such randomization may accomplished by changing thecoordinate positions of the nodes in the x, y, and z directions of aCartesian coordinate system, to new positions based on a definedmathematical function. To achieve a required external shape for a devicebeing created, these references have taught the truncation or removal ofstruts forming the unit cells at the outer surface. Such truncationhelps to achieve the near-net shape of the intended structure, buttruncated or clipped struts may, in some instances, create a situationwhere the porous geometries are un-supported by the underlyingstructures. These truncated struts may present a potential site for thegeneration of debris as protruding struts may fracture.

Additionally, although modeling structures with porous geometries hasbecome a very useful tool in modern rapid prototyping, models of aporous ingrowth structure may in some instances include a surface thatgenerates an intended structure that, prior to bone ingrowth into thestructure, leaves a gap between the porous ingrowth structure andresected bone or other bone structure with which the porous ingrowthstructure interfaces. While bone cement may be used at the time ofsurgery to provide initial stability, the application of such requiresadditional steps, risks, and time, and may interfere with the intendedbone ingrowth capabilities of the surface. Moreover, the mechanicalintegrity of the cement mantle is dependent upon surgical technique aswell as the cement material. Over a long period of time, the cement actsas an additional mechanical structure but adds additional risks due topotential failure within the cement mantle and at both the cement-boneand cement-implant interfaces.

Thus, a new method is needed to create build geometries having surfacesthat are more robust and less likely to form debris as well as thatprovide initial stability that eliminates the need for cement andreduces or eliminates these risks.

SUMMARY OF THE INVENTION

In accordance with an embodiment of the invention, a process ofpreparing a computer generated model of a three dimensional structureconstructed of porous geometries may include a step of preparing acomputer-generated component file including a porous CAD volume having aboundary having a predefined portion. The process for preparing themodel may include a step of populating, by a processor, a space. Thespace may include the porous CAD volume which may be populated by unitcells that overlap the predefined portion of the boundary. The processfor preparing the model may include a step of populating, by aprocessor, the unit cells with porous geometries. The porous geometriesmay have a plurality of struts with nodes at each of the ends of thestruts including a first strut overlapping the predefined portion of theboundary. The first strut may have a length, a first node outside theporous CAD volume, and a second node inside the porous CAD volume. Theprocess for preparing the model may include a step of removing allstruts entirely outside the porous CAD volume in which after the removalof the struts entirely outside the porous CAD volume, each of theremaining struts is connected to a node at each end of the remainingstruts.

In accordance with a further embodiment of the invention, a process ofpreparing a computer generated model of a three dimensional structureconstructed of porous geometries may include a step of preparing acomputer-generated component file including a porous CAD volume having aboundary with a predefined portion. The process may include a step ofpopulating, by a processor, a space. The space may include the porousCAD volume which may be populated by unit cells that overlap thepredefined portion of the boundary. The process for preparing the modelmay include a step of populating, by a processor, the unit cells withporous geometries in which the porous geometries have a plurality ofstruts with nodes at each of the ends of the struts including a firststrut that intersects the predefined portion of the boundary. The firststrut may have a length and a first node at a first location that may beon the predefined outer boundary or outside the porous CAD volume. Theprocess for preparing the model may include a step of removing allstruts entirely outside the porous CAD volume. The process for preparingthe model may include a step of moving the first node from the firstlocation to a second location.

In accordance with a further embodiment of the invention, a tangiblecomputer-readable storage medium may have computer readable instructionsof a program stored on the medium. The instructions, when executed by aprocessor, may cause the processor to perform a process of preparing acomputer generated model of a three dimensional structure constructed ofunit cells. The process of preparing the model may include a step ofpreparing a computer-generated component file including a porous CADvolume having a boundary having a predefined portion. The process forpreparing the model may include a step of populating, by a processor, aspace. The space may include the porous CAD volume which may bepopulated by unit cells that overlap the predefined portion of theboundary. The process for preparing the model may include a step ofpopulating, by a processor, the unit cells with porous geometries. Theporous geometries may have a plurality of struts with nodes at each ofthe ends of the struts including a first strut overlapping thepredefined portion of the boundary. The first strut may have a length, afirst node outside the porous CAD volume, and a second node inside theporous CAD volume. The process for preparing the model may include astep of removing all struts entirely outside the porous CAD volume inwhich after the removal of the struts entirely outside the porous CADvolume, each of the remaining struts is connected to a node at each endof the remaining struts.

In accordance with a further embodiment of the invention, a process ofpreparing a computer-generated model of a three-dimensional structureconstructed of porous geometries may include a step of preparing acomputer-generated component file including a porous CAD volume having aboundary. The process for preparing the model may include a step ofpopulating, by a processor, a space including the porous CAD volume withunit cells. The process for preparing the model may include a step ofpopulating, by a processor, the unit cells with porous geometries. Aplurality of the porous geometries may have a plurality of struts withnodes at each of the ends of the struts. The process for preparing themodel may include a step of populating, by a processor, the space withat least one fixation element that may extend beyond the boundary toproduce an interlocking feature. Such an interlocking feature may enableassembly or engagement with a mating structure.

In accordance with a further embodiment of the invention, a process ofproducing a three-dimensional structure may include a step of preparinga computer-generated model of a three-dimensional structure such as inthe manner just described. The process of producing the structure mayinclude a step of depositing a metal powder onto a substrate. Theprocess of producing the structure may include a step of scanning a beamonto the deposited metal powder to form a first physical layer of aporous section. The first physical layer may correspond to a portion ofa porous CAD volume of the model of the three-dimensional structure. Thethree-dimensional structure may have a geometric lattice structureconstructed of porous geometries and a boundary. The porous geometriesmay be formed by a plurality of struts. Each of the plurality of strutsmay have a node on each end of the strut. The process of producing thestructure may include a step of repeating the step of depositing themetal powder onto the substrate. The process of producing the structuremay include a step of repeating the step of scanning the beam onto thedeposited metal powder to form additional physical layers of thethree-dimensional structure. The process may include a step of formingan elongated fixation member for assembly or engagement with a matingstructure. The fixation member may correspond to the elongated fixationelement and may extend beyond the boundary.

In accordance with a further embodiment of the invention, a tangiblecomputer-readable storage medium may have computer readable instructionsof a program stored on the medium. The instructions, when executed by aprocessor, may cause the processor to perform a process of preparing acomputer-generated model of a three-dimensional structure constructed ofunit cells. The process of preparing the model may include a step ofpreparing a computer-generated component file including a porous CADvolume having a boundary. The process for preparing the model mayinclude a step of populating, by a processor, a space including theporous CAD volume with unit cells. The process for preparing the modelmay include a step of populating, by a processor, the unit cells withporous geometries. A plurality of the porous geometries may have aplurality of struts with nodes at each of the ends of the struts. Theprocess for preparing the model may include a step of populating, by aprocessor, the space with at least one fixation element that may extendbeyond the boundary to produce an interlocking feature. Such aninterlocking feature may enable assembly or engagement with a matingstructure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a functional diagram of a system in accordance with anexemplary embodiment of the present invention;

FIG. 2( a) is a three-dimensional schematic representation of two unitcells and two porous geometries located therein;

FIG. 2( b) is a three-dimensional schematic representation of a spatialarrangement of melt spots that may be used to create the porousgeometries of FIG. 2 a;

FIG. 3 illustrates a two-dimensional representation of a bounding boxcontaining unit cells in accordance with an embodiment of the invention;

FIG. 4 illustrates the unit cells of FIG. 3 separated into those thatintersect a boundary of a porous CAD volume and those that do notintersect the porous CAD volume

FIG. 5 shows the complete unit cells lying within the boundary of theporous CAD volume that are retained as shown in FIG. 4;

FIG. 6 illustrates a wireframe of porous geometries created within theretained unit cells shown in FIG. 5;

FIG. 7( a) illustrates a wireframe of porous geometries created withinthe unit cells that intersect the boundary of the porous CAD volumeshown in FIG. 4;

FIG. 7( b) illustrates the nodes of the porous geometries within theunit cells of FIG. 7( a).

FIGS. 8( a) and (b) illustrate the wireframe of the porous geometries ofFIG. 7 after clipping struts of the porous geometries at theirintersections with the boundary of the porous CAD volume;

FIGS. 9( a) and (b) illustrate the wireframe of the porous geometries ofFIG. 7 after clipping the full lengths of struts that overlap theboundary of the porous CAD volume;

FIGS. 10( a) and (b) illustrate the wireframe of the porous geometriesof FIG. 7 after clipping the full lengths of struts that lie entirelyoutside the boundary of the porous CAD volume;

FIGS. 11( a) and (b) illustrate the wireframe of the porous geometriesof FIG. 7 after clipping the full length of struts overlapping theboundary and having an inner node closest to the boundary to theirrespective inner nodes and the full length of struts lying entirelyoutside the boundary, while retaining the struts having the full lengthof struts overlapping the boundary and having an outer node closest tothe boundary of the porous CAD volume;

FIGS. 12( a) and (b) illustrate the wireframe of the porous geometriesof FIG. 11 after repositioning of the nodes closest to the boundary topositions along the boundary of the porous CAD volume through conformalmanipulation;

FIGS. 13( a) and (b) show plan and side cross-sectional views,respectively, of a solid CAD volume surrounded by a boundary of a porousCAD volume of a tapered cylindrical geometry for use in accordance withan embodiment of the invention;

FIGS. 14( a) and (b) show plan and side cross-sectional views,respectively, of the tapered cylindrical geometry of FIG. 13, whereinnodes are populated at corners of unit cells within slices of the porousCAD volume through the use of polar coordinates;

FIGS. 15( a)-(c) show a plan view including unit cells, a plan viewwithout unit cells, and a side cross-sectional view, respectively, ofthe tapered cylindrical geometry of FIG. 14, wherein struts connectingthe nodes have been generated in a conformal manner;

FIGS. 16( a) and (b) illustrate plan cross-sectional views of thetapered cylindrical geometry of FIG. 15, before and after, respectively,repositioning of the nodes circumferentially about the cylindricalgeometry at a boundary thereof in the same direction to create astructure with torque resistant properties.

FIG. 17 illustrates a plan cross-sectional view of the taperedcylindrical geometry of FIG. 16( a) after repositioning of the nodescircumferentially about the cylindrical geometry at the boundary thereofin opposite directions on opposite portions to create a structure withtorque resistant properties;

FIGS. 18( a) and (b) illustrate side cross-sectional views of thetapered cylindrical geometry of FIG. 15, before and after, respectively,repositioning of the nodes longitudinally along the cylindrical geometryat the boundary thereof to create structures with anti back-outproperties;

FIGS. 19( a)-(c) illustrate computer-generated models of cylindricalstructures created by (a) clipping struts, positioned using Cartesiancoordinates, at a boundary of a porous CAD volume, (b) positioning nodesbased on polar coordinates, and (c) positioning nodes using Cartesiancoordinates including repositioning of the nodes closest to the boundaryto positions along the boundary of the porous CAD volume throughconformal manipulation;

FIGS. 20( a)-(c) illustrate computer-generated models of structurescreated by positioning struts based on polar coordinates and thendisplacing nodes by varying amounts to create anti-back out functions;

FIG. 21 is a schematic of a surface produced by manipulating nodes inaccordance with an embodiment of the invention to create a desiredsurface roughness;

FIGS. 22( a)-(c) illustrate a process of roughening a predeterminedsurface by moving nodes within a defined region along the surface inaccordance with an embodiment of the invention;

FIGS. 23( a) and (b) show coupons having surfaces prepared by (a)applying and (b) not applying a predetermined surface roughness theretoin accordance with an embodiment of the present invention;

FIG. 24 shows a curved surface prepared by applying a predeterminedsurface roughness thereto in accordance with an embodiment of thepresent invention;

FIGS. 25( a) and (b) show examples of flat surfaces prepared by applyinga predetermined surface roughness thereto to create surface labelling inaccordance with an embodiment of the invention;

FIGS. 26( a) and (b) illustrate side elevation and plan views,respectively, of a model of a flat surface having surface nodedeformation to create irregularity in a specific area of a regularstructure in accordance with an embodiment of the present invention;

FIG. 27 shows an example of a curved surface having surface nodedeformation to create irregularity in a specific area of a regularstructure in accordance with an embodiment of the invention;

FIGS. 28( a) and (b) illustrate the wireframes of the porous geometriesof FIGS. 12 and 15, respectively, having portions of struts added to thesurface nodes of the respective porous CAD volumes;

FIG. 29 is a process flow diagram in accordance with an embodiment ofthe invention;

FIG. 30 is another process flow diagram in accordance with an embodimentof the invention;

FIG. 31 is another process flow diagram in accordance with an embodimentof the invention;

FIG. 32 is another process flow diagram in accordance with an embodimentof the invention;

FIGS. 33( a) and (b) illustrate elongated fixation elements extendingfrom the wireframe of FIG. 12 in accordance with an embodiment of theinvention;

FIGS. 34( a) and (b) illustrate elongated fixation elements extendingfrom the wireframe of FIG. 12 in accordance with an embodiment of theinvention;

FIGS. 35( a)-(c) show a plan view including unit cells, a plan viewwithout unit cells, and a side cross-sectional view, respectively, ofthe tapered cylindrical geometry of FIG. 15, wherein elongated fixationelements extend from a substrate thereof;

FIG. 36 shows a cross-sectional view of a model build structure of afemoral knee implant having elongated fixation elements extending from aporous CAD volume thereof in accordance with an embodiment of theinvention; and

FIGS. 37( a) and (b) show a portion of a model build structure of atibial knee implant having elongated fixation elements extending from asolid CAD volume thereof and through a porous CAD volume thereof inaccordance with an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

This invention relates generally to generating computer models ofthree-dimensional structures. These models may be used to prepare poroustissue in-growth structures in medical implants and prostheses. Themodels may include features corresponding to tangible structures havingnodes along a predefined outer boundary.

FIG. 1 depicts a system 105 that may be used, among other functions, togenerate, store and share three-dimensional models of structures. Thesystem 105 may include at least one server computer 110, a first clientcomputer 120, and in some instances, at least a second client computer130. These computers may send and receive information via a network 140.For example, a first user may generate a model at the first clientdevice 120. The model may then be uploaded to the server 110 anddistributed via the network 140 to the second client computer 130 forviewing and modification by at least a second user.

The network 140, and intervening communication points, may comprisevarious configurations and protocols including the Internet, World WideWeb, intranets, virtual private networks, wide area networks, localnetworks, private networks using communication protocols proprietary toone or more companies, Ethernet, WiFi and HTTP, and various combinationsof the foregoing. Such communication may be facilitated by any devicecapable of transmitting data to and from other computers, such as modems(e.g., dial-up, cable or fiber optic) and wireless interfaces. Althoughonly a few devices are depicted in FIG. 1, a typical system may includea large number of connected computers, with each different computerbeing at a different communication point of the network.

Each of computers 110, 120, and 130 may include a processor and memory.For example, server 110 may include memory 114 which stores informationaccessible by a processor 112, computer 120 may include memory 124 whichstores information accessible by a processor 122, and computer 130 mayinclude memory 134 which stores information accessible by a processor132.

The processors 112, 122, 132 may be any conventional processor, such ascommercially available CPUs. Alternatively, the processors may bededicated controllers such as an ASIC, FPGA, or other hardware-basedprocessor. Although shown in FIG. 1 as being within the same block, theprocessor and memory may actually comprise multiple processors andmemories that may or may not be stored within the same physical housing.For example, memories may be a hard drive or other storage media locatedin a server farm of a network data center. Accordingly, references to aprocessor, memory, or computer will be understood to include referencesto a collection of processors, memories, or computers that may or maynot operate in parallel.

The memories may include a first part storing applications orinstructions 116, 126, 136 that may be executed by the respectiveprocessor. The instructions 116, 126, 136 may be any set of instructionsto be executed directly (such as machine code) or indirectly (such asscripts) by the processor. In that regard, the terms “applications,”“instructions,” “steps” and “programs” may be used interchangeablyherein.

The memories may also include a second part storing data 118, 128, 138that may be retrieved, stored or modified in accordance with therespective instructions. The memory may include any type capable ofstoring information accessible by the processor, such as a hard-drive,memory card, ROM, RAM, DVD, CD-ROM, write-capable, and read-onlymemories or various combinations of the foregoing, where theapplications 116 and data 118 are stored on the same or different typesof media.

In addition to a processor, memory and instructions, client computers120, 130, 131, 133 may have all of the components used in connectionwith a personal computer. For example, the client computers may includean electronic display 150, 151 (e.g., a monitor having a screen, atouch-screen, a projector, a television, a computer printer or any otherelectrical device that is operable to display information), one or moreuser inputs 152, 153 (e.g., a mouse, keyboard, touch screen and/ormicrophone), speakers 154, 155, and all of the components used forconnecting these elements to one another.

Instructions 126, 136 of the first and second client devices 120, 130may include building applications 125, 135. For example, the buildingapplications may be used by a user to create three-dimensionalstructures, such as those described further herein. The buildingapplications may be associated with a graphical user interface fordisplaying on a client device in order to allow the user to utilize thefunctions of the building applications.

A building application may be a computer-aided design (CAD)three-dimensional (3-D) modeling program or equivalent as known in theart. Available CAD programs capable of generating such a structureinclude Autodesk® AutoCAD®, Creo® by Parametric Technology Corporation(formerly Pro/Engineer), Siemens PLM Software NX™ (formerlyUnigraphics), and CATIA® by Dassault Systèmes. Such structures may bethose described in the '421 Application.

The data 118, 128, 138 need not be limited by any particular datastructure. For example, the data may be stored in computer registers, ina relational database as a table having a plurality of different fieldsand records, or XML documents. The data may also be formatted into anycomputer-readable format such as, but not limited to, binary values,ASCII or Unicode. Moreover, the data may comprise any informationsufficient to identify the relevant information, such as numbers,descriptive text, proprietary codes, pointers, references to data storedin other memories (including other network locations) or informationthat is used by a function to calculate the relevant data. For example,the data 128 of the first client device 120 may include information usedby the building application 125 to create three-dimensional models.

In addition to the operations described above and illustrated in thefiguress, various other operations will now be described. It should beunderstood that the following operations do not have to be performed inthe precise order described below. Rather, various steps may be handledin a different order or simultaneously. Steps may also be omitted oradded unless otherwise stated herein.

An overall three-dimensional representation of a component may first begenerated by preparing a CAD model. This overall CAD model may compriseof one or more distinct CAD volumes that are intended to be manufacturedas either solid or porous geometries.

Solid CAD volumes can be sliced into layers of a predetermined thicknessready for hatching, re-merging with the porous volume (post-latticegeneration) and subsequent manufacture.

Porous CAD volumes (the basic principles of which are detailed in FIGS.2( a) and (b) can be processed using bespoke software. In this case theporous geometry is made up of a plurality of struts organized withintessellating unit cells 60. Many designs of porous geometry are possibleto impart various strength, surface, and/or other characteristics intothe porous CAD volume. For example, these porous geometries can be usedto control the shape, type, degree, density, and size of porosity withinthe structure. Such porous geometry designs can be dodecahedral,octahedral, tetrahedral (diamond), as well as many other various shapes.In comparison, dodecahedral porous geometries have a differentmechanical performance than a tetrahedral structure. Besides theseregular geometric shapes, the porous geometries of the present inventionmay be configured to have irregular shapes where various sides anddimensions have little if any repeating sequences. Porous geometries caneven be configured into constructs that closely mimic the structure oftrabecular bone. Porous geometries can be space filling, in which allthe space within a three-dimensional object is filled with porousgeometries but do not always fill the space of an object they are usedto produce.

FIG. 3 shows in greater detail a portion of a model build structure 50,generated through the use of an engineering design package such as thatdescribed previously herein.

The first step in creating a porous CAD volume is calculate a boundingbox, i.e., a box whose x, y, and z dimensions correspond to, or areslightly larger than, a defined boundary of the porous CAD volume, whichmay be the entire boundary or a portion of a boundary as shown in FIG.3. This bounding box is then divided into a number of unit cells definedby x, y, and z dimensions. Calculations are then performed during aninterrogation on each individual unit cell to ascertain if each cell iswithin, or intersects the boundary of the porous CAD volume, asillustrated by FIGS. 4 and 5. If these conditions are satisfied for anindividual cell, the cell is retained, whereas if they are not, the cellis discarded. Once all cells have been interrogated, porous geometry ispopulated within the cells that have been retained, as shown in FIGS. 6and 7).

Various building blocks make up a porous geometry. Referring again toFIGS. 2 and 3 each of the porous geometries are made up of struts 65, orsegments having a length. Nearly all of the struts 65 of the model buildstructure 50 meet at a node or intersection 70. The position of thenodes may be identified within an array of the data of the processoraccording to Cartesian, polar coordinates, or other user-definedcoordinates.

The porous CAD volume has a predefined boundary 100 that corresponds tothe intended outer surface of the part being designed. A portion of theboundary 100 is illustrated in FIG. 7. As shown, some of the unit cells60 along the predefined boundary 100 have overlapping struts 8-21 thatcross over the boundary 100. The struts 8-21 have inner nodes 26-29, 31,and 33 within the boundary 100 of the porous CAD volume and outer nodes25, 30, 32, 34, and 35 outside of the boundary 100.

To produce a porous structure having struts that terminate along theboundary, the overlapping struts may be clipped such that any portion ofthe overlapping struts beyond the predefined boundary is removed. FIG. 8depicts a model build structure 50 generated according to this clippingapproach, in other words, after the overlapping struts 8-21 have beenclipped. The overlapping struts 8-21 are now shorter. The ends of eachof the overlapping struts 8-21 now lie along the predefined outerboundary 100 and none of the overlapping struts 8-21 extend past theboundary 100.

In some cases this clipping approach may be appropriate. However, thestruts that have been shortened may not be supported at their outerpoints as can be seen in the model of FIG. 19( a), and as such they canact as cantilevers and may result in an increased risk of debrisformation. In some instances (assuming a flat edge is present), theporous CAD volume may be modified so that the boundary lies along awhole number of unit cells. In this instance there is no need for theclipping operation. This mitigates the possibility of debris generationas the end of each strut is supported by at least one other strut, andis correspondingly less prone to failure.

FIG. 9 shows the model build structure 50 prepared by another approachwhere the full length of struts that overlap the surface of the porousCAD volume are removed to the inner node. Thus the overlapping struts8-21 are removed. Preferably, removal of these struts leaves only thecomplete porous geometries 60. However, this approach may leave thesurface rough, uneven and nonconforming to the original porous CADvolume as some of the unit cells 60 do not reach the outer boundary 100.

FIG. 10 shows the model build structure 50 prepared by another approachwhere the full length of struts that overlap the surface of the porousCAD volume are retained to their respective outer nodes. In this manner,the overlapping struts 8-21 remain beyond the boundary 100 of the porousCAD volume.

FIG. 11 shows the model build structure 50 prepared by yet a furtherapproach where each of these struts 8-21 are either fully retained orfully removed, depending on the distance of their nodes from theboundary 100 of the porous CAD volume. In the example shown, each of theunit cells 60 outside the outer boundary 100 as well as the struts 9-12,16 and 19 are removed (or marked for removal). The struts selected forremoval are those overlapping struts in which the node outside theboundary, i.e., the outer node, is further from the boundary than thecorresponding node of the overlapping strut inside the boundary, i.e.,the inner node. In contrast, the overlapping struts 8, 13-15, 17-18, and20-21 are not removed because their corresponding nodes 25, 30, 32, 34,and 35, although outside the outer boundary 100 are closer to theboundary 100 than their corresponding inner nodes.

FIG. 12 shows the model build structure 50 prepared after clipping,followed by the repositioning of the remaining nodes 25-35, closest tothe boundary 100 of the porous CAD volume to coincide with the boundary100. In some embodiments, each of the nodes 25-35 closest to theboundary 100 may be repositioned to a location determined by amathematical calculation based on the original position of each of thesenodes, e.g., the distance from the boundary of each of these nodes, orthe original length of the struts attached to these nodes that overlapthe boundary or both of these values. In this manner, the shape of thestructure may be maintained when having nodes along the boundary.

As further shown in FIG. 12, when the nodes 25-35 are repositioned, theremaining struts connected to the nodes 25-35 may then be lengthened orshortened as required to maintain connectivity between the nodes. Inthis manner, the outermost nodes and struts may be positioned such thatthey do not coincide with the boundary by any function of the cell sizeor geometry. This effect can be seen clearly in FIG. 19( c).

In a variant of this embodiment, the nodes 25-35 may not be moved butinstead discarded and replaced by new nodes. Additionally, the strutsconnected to the nodes 25-35 may be replaced by new struts that arelonger or shorter than the original struts to maintain the connectivitybetween the nodes.

The use of polar or spherical coordinates to define nodes may bepreferred to the use of Cartesian coordinates when a surface of a modelbuild structure to be formed is curvate or cylindrical. In this manner,nodes repositioned on a boundary may be positioned at the same angledefining a replaced node but at a different radius from the origin of apolar coordinate system being used to create a model build structure.However, other user-defined coordinates may be used to create conformalstructures. In other words, a user-defined node positioning system maybe used to form a model build structure having nodes along an outerboundary that fit the contours of the outer boundary of the componentbeing modeled.

FIG. 13 shows various cross sections of a tapered, cylindrical geometry.The gray color represents the solid CAD volume which is bounded by aclear, porous CAD volume.

FIG. 14 further shows the geometry of FIG. 13 subsequent to thegeneration of a plurality of outer nodes 410 and a plurality of innernodes 430 along inner and outer boundaries 435, 445 of the porous CADvolume. Such nodes define the vertices of unit cells 450 which arecreated by virtually slicing the porous CAD volume according to the unitcell height. This operation produces polar rings that are then populatedwith volumes that pattern radially around the ring of the part. Thesevolumes define the unit cells for the part.

FIG. 15 shows the population of the unit cells 450 created in theprevious stage. The depicted geometry is based on the preferredoctahedral cell as described previously herein but could be based on anyporous geometry. These porous geometries are then defined by nodes withconnecting struts or segments 480, all of which meet at the definedsurface of the porous CAD volume 500. This effect can be seen clearly inFIG. 19( b).

Creation of beneficial surface properties can be achieved through themovement of the nodes 410 at the outer surface 500 of the porous CADvolume. FIGS. 16 and 17 detail the creation of torque or movementresisting features on the surface of cylindrical components. The nodes410-427 that lie on the outermost boundary of the porous CAD volume 500can be manipulated to be repositioned along the surface of the porousCAD volume 500 in either direction to create a deformed unit cell with apreferential direction of movement. Such manipulation involves thechanging of the coordinate positions of the nodes. For example, theangular component of at least some of the polar coordinates of the nodesalong the boundary may be modified in the same or opposite directions toproduce an anti-torque effect. In another example, the height componentand in some instances the radius component as well of the nodes alongthe boundary may be modified in the same or opposite directions toproduce an anti-backout effect. In producing either of these effects,the struts may correspondingly be lengthened or shortened as necessaryto maintain connectivity with the nodes along the boundary. The amountthat any coordinate is changed can be based on any empirical ormathematical function.

A similar modification in the vertical direction is shown in FIG. 18. Inthis case the nodes on the outermost boundary of the porous CAD volume500 are manipulated to be repositioned in the vertical direction tocreate features that are resistant to the part being extracted afterinsertion.

In another example, as illustrated in FIG. 21, surface features can begenerated on any part where the surface is made up of connected nodes.Intrinsic surface properties can be created through the movement ofnodes away from the surface to positions both inside and outside of theporous CAD volume. The location of the new position of a node 151-160and corresponding struts 161-170 may be a parameter of the buildingapplication such that the repositioned node 151-160 will be at aposition selected to satisfy a predetermined theoretical surfaceroughness along the predefined portion of the outer boundary 200. Thetheoretical surface roughness may be defined by a formula for surfaceroughness, such as any of the ANSI/ASME B46.1-2009 standards for surfaceroughness R_(a), R_(s), R_(z), or R_(q). In addition, the new positionsof a group of nodes 151-160 and corresponding struts 161-170 along apredefined portion of the outer boundary 200 may be selected such thatthe surface roughness of the predefined portion of the outer boundary200 is a predetermined value. Thus, the positions chosen may be selectedat random so long as the aggregate of the positions of the nodes 151-160and corresponding struts 161-170 satisfy the theoretical surfaceroughness chosen. For example, if R, is the parameter, then each of thestruts 161-170 and nodes 151-160 along the outer boundary 200 must fallwithin a set distribution between minimum and maximum heights 275 and285, respectively, as shown in FIG. 21.

FIGS. 23( a) and (b) depict the surfaces of flat structures formed usinga conventional modeling method and some of the approaches describedherein. FIG. 23( a) is a photograph of a coupon formed by selectivelaser melting of powdered metal prepared in accordance with a methodknown in the prior art. To produce the coupon, a model build structurewas prepared with the upper nodes of the regular, octahedral, porousgeometry deliberately intersecting the upper surface boundary of thecuboid porous CAD volume.

FIG. 23( b) is a photograph of another coupon formed using the sameselective laser melting process as the coupon in FIG. 23( a). The modelbuild structure used to produce the coupon in FIG. 23( b) used the samelattice structure as the coupon in FIG. 23( a). However, an approach inaccordance with those described herein was employed to produce the topsurface of the model build structure corresponding to the roughened topsurface 200 shown in FIG. 23B. An algorithm was applied to the nodes atthe upper surface of the porous CAD volume. This algorithm required apredetermined surface roughness (to a corresponding R_(a), S_(a) orother standard roughness measure) as described previously. FIG. 23( b)shows the resultant built geometry illustrating the surface roughnessobtained.

The features previously described herein can be used on any surface. Anexample of their use on curved surfaces is shown in FIG. 22. A porousCAD volume that conforms to a surface 100 is used as the base. An upperbound 300 and lower bound 301 define a region 302 in which the surfacenodes 25-35 can be repositioned. As in the example shown in FIGS. 8( a)and 8(b), the amplitude and direction of each movement can be controlledto create any predetermined theoretical surface quality e.g., roughnessor surface marking. This same algorithm has been applied to a curvedsurface detailed in FIG. 24 where the nodes have been moved by a setamplitude to get a desired roughness value on a curved surface.

Specific use can be made of these different roughening algorithms toproduce desired effects, for example surface marking for use in productidentification. This can be seen in FIG. 25 which illustrates that it ispossible to produce markings that are invisible under normal light, andvisible under angular directed light, for example by creating areas ofdifferent roughness, which may be sub-flush or proud of the surface.This could also be applied in the form of a 2-D barcode or QR code thatmay contain proprietary information relating to the specific implant towhich the coding has been applied. In this manner, the marking may bereadable by hand-held laser scanners or other well-known devices.

Another application of the movement of the nodes along and through thesurface is demonstrated in FIG. 26. These relate to the creation of anirregular appearance at the surface of a regular structure. The nodesthat are at the surface can be moved along, out of, into or in anycombination of these movements to create a modified surface that hasirregular qualities but which is based on a regular structure.

Yet a further method of creating surface roughness is shown in FIG. 28.Additional struts 80 may be added onto the outer nodes 25-35 as definedin the arrangement shown in FIG. 12, and additional struts 520 may beadded onto outer nodes 410-427 as defined in the arrangement of FIG. 16.These additional struts do not connect to another strut. In this manner,these struts may give rise to a resistance to movement in a direction atan angle sufficiently perpendicular to the surface.

As contemplated by an embodiment of this invention, self-retainingfeatures, such as the additional struts 520, may be used to produce a“VELCRO” type effect in tangible structures formed from a correspondingmodel build structure. In this manner, the outside surface of onetangible structure having a self-retaining feature may be an inverserepresentation of the outside surface of a mating tangible structurehaving a corresponding self-retaining feature. For example, the matingstructures may each have additional struts that interlock or engage withone another. In other embodiments, additional struts of one structuremay fit into pores or holes on the surface of another structure in a“hook and eye” formation or through an interference fit to attach thetwo structures. As shown in FIGS. 33( a) and (b), elongated fixationelements 580 may be substantially parallel to each other and extend fromthe outer nodes 25-35. In the example shown, the fixation elements 580are additional struts incorporated into the model build structure thatare only connected to the model build structure at one node in which theother end of the fixation elements lies outside the boundary 100.

The fixation elements 580 may correspond to “microspikes” of an intendedphysical structure that are created using the model of the elements 580.The microspikes may mesh in an interference fit with another matingstructure which may have receiving holes for the microspikes or whichmay be soft enough to permit the microspikes to puncture through asurface of the structure. For instance, the microspikes preferably maybe capable of piercing through a bone surface, in particular a spongybone surface. The elements 580 may extend in a predetermined directionrelative to the boundary 100. When used in this manner, at least aportion of the fixation elements 580 preferably may be substantiallyparallel to each other such that the portion of the substantiallyparallel fixation elements has a density within a plane perpendicular tothe fixation elements 580 of approximately 20 to 400 elements per squarecentimeter, and more preferably approximately 50 to 200 elements persquare centimeter. Such densities may provide sufficient surface contactbetween the physical porous structure corresponding to the porous CADvolume and a mating structure in which the fixation elements may beinserted to maintain an interlock between the physical and matingstructures. When a portion of the fixation elements 580 aresubstantially parallel to each other, the fixation elements 580 also maypreferably be spaced a distance from each other that is larger than thelargest pore diameter of the bone.

The fixation elements 580 may extend in a number of predetermineddirections relative to the boundary. In some arrangements, the fixationelements 580 may be perpendicular to the boundary 100. As shown in theexample of FIGS. 33( a) and (b), the elements 580 may extend, in someinstances, in a direction that is different from the direction of struts581 that intersect with struts forming the boundary of the porous CADvolume. The fixation elements 580 preferably may form an angle of 10° to90°, and more preferably may form an angle of 30° to 90°, with theboundary 100. Typically, the predetermined direction of fixationelements 580 intended to be mated with a structure will be substantiallyparallel to the direction of a seating area of a mating structure intowhich the fixation elements 580 are adapted to be received.

In accordance with another embodiment, with specific reference to FIGS.34( a) and (b), adjacent struts 685, 686 may be attached to the porousCAD volume, extending from the outer nodes 25-35 on one end and beattached to each other on the other end at nodes 1027-1035 to formportions of a plurality of elongated fixation elements 690. For example,strut 685 may extend from node 335 on one end to node 1035 on the otherend. Likewise, strut 686 may extend from node 34 on one end to node 1035on the other end. Similarly, other adjacent struts 685, 686 along theboundary 100 may extend from the porous CAD volume and connect to eachother.

It should be noted that FIGS. 33( a) and (b) and FIGS. 34( a) and (b)only illustrate a two-dimensional slice of a portion of the porous CADvolume. Accordingly, in the example of FIG. 34, two or more other struts(not shown) may be connected to both strut 685 and strut 686 to formother sides of a fully connected porous geometry (e.g., formed using atetrahedron unit cell as described previously herein) that form theelongated fixation element 690. The fixation element 690 may be morespace-filling, but may also provide greater bending and torsionalstrength than the fixation elements 580 shown in FIG. 33. Thesespace-filling fixation elements may also provide for interference fitswith mating structures. Due to their greater surface area for contactinga mating structure, these fixation elements may also provide for greateradhesion to a mating structure than fixation elements, such as elongatedfixation elements 580.

As in the example shown in FIGS. 34( a) and (b), the fixation elements690 may have a longitudinal axis extending between each of the connectedstruts extending from the porous CAD volume. Moreover, as in thearrangement shown, the longitudinal axes of the fixation elements 690may be substantially parallel to each other along at least a portion ofthe boundary 100. In such a configuration, the fixation elements 690preferably may have a density within a plane perpendicular to thelongitudinal axes through the fixation elements 690 of approximately 20to 500 elements per square centimeter, and more preferably approximately50 to 300 elements per square centimeter.

In the views shown in FIGS. 35( a)-(c), elongated fixation elements 790are formed by struts 785 and 786 and two other struts (not shown) in amanner similar to that described for the fixation elements 690. Incontrast with the fixation elements 690, however, the fixation elements790 extend from a solid CAD volume 795. In this manner, the fixationelements 790 extend from nodes 791 formed at the interface of the solidCAD volume 795 and a porous CAD volume 780. Moreover, in the arrangementshown, fixation elements 790 are formed such that a longitudinal axisthrough the fixation elements is perpendicular to a plane tangential tothe solid CAD volume 795 at an imaginary point of intersection betweenthe longitudinal axis and the solid CAD volume 795. Accordingly, whenused in the tapered cylindrical geometry shown in the views of FIGS. 35(a) through (c), the elongated fixation elements 790 extend from thesolid CAD volume 795 such that the longitudinal axes of fixationelements 790 within a given plane around the circumference of the modelbuild structure are not parallel.

As shown in FIG. 36, a model build structure of a femoral knee implant1100 may be formed in the manner described previously herein such that aporous CAD volume 1180 is mated to a solid CAD volume 1195 at aninterface 1185. As shown, elongated fixation elements, such as thefixation elements 1191, 1192 may extend from the porous CAD volume 1180such that the longitudinal axes through at least some of the elongatedfixation elements is not parallel. In this manner, the fixation elementsmay be used to create microspikes of the intended implant thatcorrespond to the fixation elements which resist movement of the implantin multiple directions to secure the implant against a patient's femur.In alternative arrangements, the fixation elements may extend from thesolid CAD volume 1195 at the interface 1185 in a manner similar to theextension of the fixation elements 790 shown in FIGS. 35( a)-(c). In theexample of FIG. 36, the fixation elements may be portions of fullyconnected porous geometries, such as those shown in FIGS. 34( a) and (b)and FIGS. 35( a)-(c), although other shapes of fixation elements may beused such as single struts, like those shown in FIG. 33.

As is shown by the portion of a model build structure used for a tray ofa tibial knee implant 1200 in FIGS. 37( a) and (b), fixation elements1290 may be formed to extend from a solid geometry 1295. In this manner,when an intended physical structure is formed using a rapid prototypingprocess as described further herein, the fixation elements 790 may bebuilt, such as through powder metal processes, directly onto asubstrate. Furthermore, the fixation elements 1290 may additionally beformed such that they extend through a porous CAD geometry 1280. In thismanner, a porous ingrowth structure (corresponding to and built usingthe porous CAD geometry 1280) may provide structural support along aportion of microspikes (corresponding to and built using the fixationelements 1290) during sideloading against the microspikes.

Still other formations along the surface of the porous CAD volumeinclude a barbed geometry with corresponding ends, a hooked geometrywith corresponding ends, deformable loops, or variations in the depth ofthe roughening applied to mating surfaces as described previouslyherein, to create an interlock between the mating surfaces. In someinstances, these types of positive engagement may remove or minimize theneed for mechanical fixation devices such as bone screws or otherassembly devices.

Other variations of the fixation elements and corresponding microspikesalso may be used. The microspikes may be formed using other shapes ofunit cells, e.g., octahedral, dodecahedral, etc. The fixation elementsand corresponding microspikes may have various shapes and sizes incomparison to other structures having these features. Moreover, variousshapes and sizes of fixation elements and microspikes may be used atdifferent portions of the surface of a corresponding CAD geometry orcorresponding intended physical structure, respectively. Furthermore,the microspikes and corresponding fixation elements may or may not beused in conjunction with additional engineering structures andrespective models thereof, such as keels, pegs, stems, and spikes, foradditional device stabilization. Such engineering structures may beintegral, i.e., form part of a monolithic structure, with or may beseparately added or fixed to, e.g., by fasteners, to intended physicalstructures. When used in conjunction with additional engineeringstructures, the fixation elements and corresponding microspikes mayextend from the additional engineering structures themselves as well asfrom other portions of the respective model build structure and intendedphysical structure. Although the formation and use of fixation elements(and corresponding microspikes) have been described with respect to afemoral and tibial knee implants, such features may be used in theproduction of other prosthetic devices such as acetabular, patella,shoulder glenoid, finger, and ankle implants, or the like.

A flow diagram shown in FIG. 29 details an embodiment of the creation ofporous geometries within a Cartesian coordinate defined unit cell. Atblock 610, a computer-generated model of a three-dimensional structureis prepared. A bounding box is created by a processor. This bounding boxis populated with unit cells 620.

The spatial interaction of the unit cells with the surface of the porousCAD volume is determined, by a processor, and two pathways are createdat a step 630. The unit cells that do not make contact with the surfaceare then interrogated to determine their position at a step 640. Unitcells that lie outside the structure are discarded. Unit cells that arewithin the porous CAD volume are populated with porous geometries 650.

The unit cells that cross the surface of the porous CAD volume arepopulated with porous geometries. The struts of porous geometries canthen either be clipped to the surface at a step 670 or clipped to a nodeat a step 680 as described previously herein. In other words, the strutsmay be clipped to an inner node, an outer node, or at the boundary ofthe porous CAD volume. However, this approach may leave the surfacerough, uneven, and nonconforming to the original porous CAD volume.

Through steps 690-692, the nodes at the surface can also be manipulatedso that all the surface nodes lie on the outer boundary of the porousCAD volume to create a conformal surface.

A process flow diagram shown in FIG. 30 details an embodiment of thecreation of porous geometries within polar or cylindrical coordinatedefined unit cells. At a step 710, a computer-generated model of athree-dimensional structure is prepared or a part is defined usinggeometric parameters.

This model may then be sliced virtually at a step 720 to produce polarrings that can then be populated with unit cells and nodes in a radialpattern at a step 730. These unit cells may be populated with porousgeometries at a step 740.

A process flow diagram shown in FIG. 31 details an embodiment thecreation of surface features through repositioning of nodes that lie onthe boundary of the porous CAD volume. This operation can be performedon any porous geometry that consists of struts which interconnect atnodes along the boundary of the porous CAD volume.

At least one node is selected at a step 810 which can then be perturbedin a variety of ways to generate the desired surface properties. In oneembodiment, a node along the boundary can be repositioned along aposition vector which is at an angle to the surface direction as shownat steps 830-831. This process may be used to create surface propertiessuch as surface roughness.

In another embodiment, a node can be moved along a position vectorparallel to the surface direction across the surface which can be usedto create torque or movement resisting, pullout resisting and surfaceirregularity properties at steps 840 and 841.

In yet another embodiment, any combination of the steps 830 and 840 maybe used to create surface properties. Nodes can be moved both along andaway from the surface to create areas of irregularity, roughness andmarking at steps 850 and 851.

In another example as shown in FIG. 32, a computer-generated componentfile is prepared at a block 910. The component file includes a porousCAD volume with a boundary having at least one predefined portion. At ablock 920, a space that includes the porous CAD volume is populated, bya processor, with unit cells that overlap the predefined portion of theboundary. Such a space may be defined by sets of coordinates, such asCartesian, polar, or spherical coordinates. At a block 930, the unitcells are populated with porous geometries. Within the porous geometriesmay be a plurality of struts. At least one end of the struts may have anode. As further shown at block 930, at least one of the struts overlapsthe predefined portion of the boundary. Such a strut has a length, onenode outside the porous CAD volume, and one node inside the porous CADvolume. At block 940, any struts entirely outside the predefined portionof the boundary are removed. In some embodiments, any struts outside theentire boundary are removed. In this manner, a computer-generated modelof a three-dimensional structure constructed of porous geometries isprepared. At an optional block 950, a tangible three-dimensionalstructure having a shape corresponding to the computer-generated modelmay be produced. The shape of the three-dimensional structure may be inthe form of a geometric lattice structure.

Visualization of all of the above effects under consideration can beachieved by voxelating the sliced output files from bespoke softwarethat is being applied in an additive layer manufacturing machine.Utilizing developed algorithms and the output files, the data may be fedinto a commercial software package, e.g., Matlab, and the imagesproduced can be interpreted. FIGS. 2( a) and 2(b) illustrate an initialprocess operation in contrast to FIGS. 19, 20 and 26 representing commonoutput images.

The approaches for generating three-dimensional models described hereinmay be used for building various tangible structures and surfaces,specifically structures and surfaces for medical implants. Although abrief summary follows, many details of the process of melting powderedmetal are given in the '421 and '327 Applications. In constructing atangible structure from a model build structure, a layer of metalpowder, in some instances, may be deposited on a substrate. Thesubstrate may be a work platform, a solid base, or a core, with the baseor core being provided to possibly be an integral part of the finishedproduct.

The metal powder may be Ti alloys, stainless steel, cobalt chromealloys, Ta or Nb. In some embodiments, individual layers of metal may bescanned using a directed high energy beam, such as a laser or e-beamsystem to selectively melt the powder, i.e., melt the powder inpredetermined locations. Each layer, or portion of a layer, is scannedto create a plurality of predetermined porous geometries by pointexposure to the energised beam. This leads to the production of strutsthat correspond to the struts described previously herein, as will bedescribed below. Successive layers are deposited onto previous layersand also are scanned. The scanning and depositing of successive layerscontinues the building process of the predetermined porous geometriesand oblique struts are directed to nodes. As disclosed herein,continuing the building process refers not only to a continuation of aporous geometry from a previous layer but also a beginning of a newporous geometry as well as the completion of the current porousgeometry.

In a preferred aspect of the present invention, the high energy beam maybe adjusted to modify the cross-sectional diameter of various struts.Some of the struts of the porous geometries may overlap struts of otherporous geometries as a result of randomization within unit cells, butsuch struts never lose their identity with respect to their origin.Dimensions of strut diameter and unit cell size may enable the adjustingof the porosity throughout the completed structure. The strut diameterpreferably should be nominally two times the diameter of the high energybeam, and each unit cell should have sides with lengths preferably nogreater than 2 mm and have an aspect ratio that is limited to a maximumof 1:2 with respect to a maximum height of the unit cell.

In some embodiments, a component structure or sub-structure thereofproduced by the approaches herein may be porous and if desired, thepores can be interconnecting to provide an interconnected porosity. Insome embodiments, the amount and location of porosity may bepredetermined, and preferably lie in the range 50% to 90% as beingsuitable when used as a bone ingrowth surface, and 20% to 90% as beingsuitable for polymer interlock surfaces. This also applies to caseswhere the outer porous section of a medical device is connected to hostbone with bone cement or bone type adhesives for example. A base or coreof cobalt chrome alloy, titanium or alloy thereof, stainless steel,niobium and tantalum, may be used to build a porous layer of any one ofthese metals and/or alloys by melting using high energy beam, such as acontinuous or pulsed laser beam or an electron beam. Thus, a mixture ofdesired mixed materials can be employed. The porous layers can beapplied to an existing article made from cobalt chrome, titanium oralloy, stainless steel, tantalum or niobium, such as an orthopaedicimplant. It is thus intended that the approaches described herein may beexploited to produce commercially saleable implants with bone in-growthstructures having porous surfaces with a controllable texture or surfaceprofile. Such an implant may be an acetabular component, a knee tibialor patella implant, a femoral knee or hip implant, or the like. Theconstructed medical implant may have a porosity and architectureoptimised, to create very favourable conditions so that bone in-growthtakes place in a physiological environment and the overall outcomefavours long-term stability.

The medical implants, as well as other constructed structures, may beprovided with an attaching mechanism for anchoring or at least morefirmly attaching the medical implant to another element. One suchexample is an acetabular component being provided with a surfacestructure which mates with the surface of an augment component.

Because a laser melting process may not require subsequent heattreatment or the temperature at which this heat treatment occurs islower than any critical phase change in the material, the initialmechanical properties of any base metal to which a porous structure isapplied may be preserved.

The equipment used for the manufacture of such a device could be one ofmany currently available including but not limited to those manufacturedby Renishaw, SLM Solutions, Realizer, EOS, Concept Laser, Arcam and thelike. The laser or electron beam may also be a custom producedlaboratory device.

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present invention as defined by the appended claims.

1. A method of preparing a computer-generated model of athree-dimensional structure constructed of porous geometries, the methodcomprising: preparing a computer-generated component file including aporous CAD volume having a boundary; populating, by a processor, a spaceincluding the porous CAD volume with unit cells; populating, by aprocessor, the unit cells with porous geometries, a plurality of theporous geometries having a plurality of struts with nodes at each endthereof; and populating, by a processor, the space with at least oneelongated fixation element extending beyond the boundary to produce aninterlocking feature to enable assembly or engagement with a matingstructure.
 2. The method of claim 1, at least one of the unit cellsincluding at least a first strut intersecting a second strut at a firstnode, wherein the elongated fixation element intersects the first node.3. The method of claim 2, wherein the elongated fixation element extendsin a predetermined direction relative to the boundary.
 4. The method ofclaim 1, wherein the elongated fixation element extends in apredetermined direction relative to the boundary.
 5. The method of claim1, further comprising: populating the porous CAD volume, during the stepof populating the space including the porous CAD volume with unit cells,with at least one unit cell overlapping the boundary; populating atleast one porous geometry, during the step of populating the unit cellswith porous geometries having a plurality of struts with nodes at eachend thereof, with a first strut overlapping the boundary, the firststrut having a length, a first node outside the porous CAD volume, and asecond node inside the porous CAD volume; and removing all strutsentirely outside the porous CAD volume; and connecting any of theremaining struts not connected to a node at each end thereof to anadjacent strut such that each of the remaining struts has a node at eachend thereof.
 6. The method of claim 1, wherein the fixation elementintersects the boundary.
 7. The method of claim 1, wherein the componentfile further includes a solid volume contacting the porous CAD volume,and wherein, the elongated fixation element extends from the solidvolume through the porous CAD volume.
 8. The method of claim 5, whereinthe component file further includes a solid volume contacting the porousCAD volume, and wherein, the elongated fixation element extends from thesolid volume through the porous CAD volume.
 9. The method of claim 1,further comprising populating, by a processor, at least a secondelongated fixation element extending beyond the boundary, wherein thefirst and second elongated fixation elements are substantially parallel.10. The method of claim 1, further comprising populating, by aprocessor, at least a second elongated fixation element extending beyondthe boundary, wherein the first and second elongated fixation elementsare substantially nonparallel.
 11. The method of claim 4, furthercomprising populating, by a processor, a plurality of elongated fixationelements extending beyond the boundary in a direction perpendicular tothe boundary, each of the plurality of elongated fixation elementsdefining corresponding longitudinal axes therethrough, wherein theplurality of fixation elements are substantially parallel, and whereinthe intersections of the longitudinal axes of the fixation elements andthe boundary have a density lower than the porosity of the matingstructure.
 12. The method of claim 1, wherein the fixation element has across-section along a length thereof that is one of substantially (i)cylindrical, (ii) rectangular, (iii) triangular, (iv) hexagonal, and (v)octagonal.
 13. The method of claim 1, wherein the fixation element istapered along a length thereof.
 14. The method of claim 1, wherein thefixation element has a helical exterior along a length thereof.
 15. Amethod of producing a three-dimensional structure comprising: preparinga computer-generated model of a three-dimensional structure according toclaim 1; depositing a metal powder onto a substrate; scanning a beamonto the deposited metal powder to form a first physical layer of aporous section corresponding to a portion of the porous CAD volume ofthe model of the three-dimensional structure, the three-dimensionalstructure having a geometric lattice structure constructed of porousgeometries and a boundary, the porous geometries formed by a pluralityof struts, each of the plurality of struts having a node on each endthereof, repeating the step of depositing the metal powder onto thesubstrate; repeating the step of scanning the beam onto the depositedmetal powder to form additional physical layers of the three-dimensionalstructure; and forming an elongated fixation member for assembly orengagement with a mating structure, the fixation member corresponding tothe elongated fixation element and extending beyond the boundary. 16.The method of producing a three-dimensional structure according to claim15, wherein the beam is at least one of (i) an electron beam and (ii) alaser beam.
 17. The method of claim 15, wherein the step of forming theelongated fixation element comprises the steps of: depositing a metalpowder onto one of the (i) substrate and (ii) porous section; scanning abeam onto the deposited metal powder to form a first physical layer ofthe elongated fixation element; repeating the step of depositing themetal powder onto the one of the (i) substrate and (ii) porous section;repeating the step of scanning the beam onto the deposited metal powderto form additional physical layers of the elongated fixation element.18. The method of claim 15, wherein the elongated fixation elementextends in a direction perpendicular to the boundary, furthercomprising: populating, by a processor, at least a second elongatedfixation element extending beyond the boundary in a directionperpendicular to the boundary, wherein the first and second elongatedfixation elements are substantially parallel; and forming a secondelongated fixation member for assembly or engagement with a matingstructure, the second fixation member corresponding to the secondfixation element, and the second fixation element further extendingbeyond the boundary, wherein the first and second elongated fixationmembers are substantially parallel.
 19. The method of claim 15, whereinthe elongated fixation element extends in a direction perpendicular tothe boundary, further comprising: populating, by a processor, at least asecond elongated fixation element extending beyond the boundary in adirection perpendicular to the boundary, wherein the first and secondelongated fixation elements are substantially nonparallel; and forming asecond elongated fixation member for assembly or engagement with amating structure, the second fixation member corresponding to the secondfixation element, and the second fixation element further extendingbeyond the boundary, wherein the first and second elongated fixationmembers are substantially nonparallel.
 20. The method of claim 19,wherein the porous section is a porous bone-ingrowth structure of afemoral knee implant having at least an anterior surface and ananteriolateral chamfer surface adjacent thereto, the first elongatedfixation element extends from the anterior surface, and the secondelongated fixation element extends from the anteriolateral chamfersurface.
 21. A tangible computer-readable storage medium on whichcomputer readable instructions of a program are stored, theinstructions, when executed by a processor, cause the processor toperform a method of preparing a computer-generated model of athree-dimensional structure constructed of unit cells, the methodcomprising: preparing a computer-generated component file including aporous CAD volume having a boundary; populating, by a processor, a spaceincluding the porous CAD volume with unit cells; populating, by aprocessor, the unit cells with porous geometries, a plurality of theporous geometries having a plurality of struts with nodes at each endthereof; and populating, by a processor, the space with at least oneelongated fixation element extending beyond the boundary to produce aninterlocking feature to enable assembly or engagement with a matingstructure.